1. Field of the Invention
The present invention relates to an ultrasonic motor which employs ultrasonic waves for providing driving impulse.
2. Description of the Related Art
An ultrasonic motor which employs ultrasonic waves for providing driving impulse has been proposed, for example, in U.S. Pat. No. 5,204,577. The ultrasonic motor of this publication, as shown in FIG. 10 of the present application which is a partial cross section through a circularly symmetric structure, comprises a ring shaped stator assembly 1 comprising a elastic body la on the lower surface of which a piezoelectric element 1b is bonded, and a ring shaped rotor assembly 2 comprising a rotor base member 2a on the lower surface of which a ring shaped slider member 2b is bonded. The slider member 2b of the rotor assembly 2 is pressed into sliding contact against a ring shaped driving surface 1c of the elastic body la of the stator assembly 1 by a pressing force in the downward direction in the figure which is transmitted from a biasing means which is not shown to the rotor base member 2a via a flange portion 2c. The width a in the radial direction of the contact surface 2d of the slider member 2b against the driving surface 1c of the stator assembly 1 is made to be less than the total width b of the rotor base member 2a in the radial direction. By doing this, the rotational performance of the rotor assembly 2 is improved. A composite resin material such as polytetrafluorethylene in which glass fiber and molybdenum disulfide are mixed has been proposed as a material of which the slider member 2b may desirably be composed. A metallic material such as aluminum alloy or the like is generally used for the rotor base member 2a in order to suppress the damping of vibrations set up therein. The reference numeral 1d denotes a flange portion for supporting the stator assembly 1.
In the ultrasonic motor shown in FIG. 10, the slider member 2b is formed to be as thin as possible, in order to suppress the damping of vibrations set up in the rotor base member 2a. Because of this, and because the slider member 2b is formed with the width a in the radial direction of its contact surface 2d narrow, the process of manufacture of the slider member 2b and the process of bonding it to the rotor base member 2a become difficult, so that the yield of these manufacturing processes becomes low, and it is impossible to reduce the cost of manufacture of the ultrasonic motor.